Musharraf came to power in 1999 by toppling the then government led by Sharif and ruled till 2008, when he was forced to resign after the PPP-led coalition threatened him with impeachment.
He remained in self-exile for about five years and returned to Pakistan in March to contest poll.
But he was hauled to courts in different cases, including one over the assassination of former premier Benazir Bhutto in 2007.
He has secured bail in all four major cases against him so far.
However, the trial for high treason poses the biggest challenge to the former commando of the Pakistan Army.
The case could linger for months before any final verdict is announced and analyst believe it could potentially derail the democratic set-up if the powerful military decides to step in and save its former chief from pubic disgrace and punishment.
